I'm not sure if you really have to but why wouldn't you? If you have the same setup as I do, your blower sits right on top of the tensioner and it only takes 3 bolts to remove the blower mount out of the way then the tensioner is easy to get at.
I just replaced my tensioner on my 2004 GT with a Vortech. I took off the supercharger it really ins't that hard after you have done it a few times. There are four bolts and its off and mine has a little more to disconnect since I have an intercooler. Trust me when replacing the tensioner do not buy one from NAPA, Pep Boys, etc. get the OEM Ford Piece. I bought one from Napa and I could move the torsional spring in the tensioner by hand but that was impossible with the OEM Ford tensioner. The Ford tensioner is much more heavy duty and you don't want any belt slip, missalignment, or breakage. I broke 2 belts in a month before realizing the problem and that requires you to pull the SC off and you are stranded for the time being. Also torque the tensioner bolt to 89 inlbs plus a 90 degree turn.